UBXN1 interferes with Rig-I-like receptor-mediated antiviral immune response by targeting MAVS.
ABSTRACT: RNA viruses are sensed by RIG-I-like receptors (RLRs), which signal through a mitochondria-associated adaptor molecule, MAVS, resulting in systemic antiviral immune responses. Although RLR signaling is essential for limiting RNA virus replication, it must be stringently controlled to prevent damage from inflammation. We demonstrate here that among all tested UBX-domain-containing protein family members, UBXN1 exhibits the strongest inhibitory effect on RNA-virus-induced type I interferon response. UBXN1 potently inhibits RLR- and MAVS-induced, but not TLR3-, TLR4-, or DNA-virus-induced innate immune responses. Depletion of UBXN1 enhances virus-induced innate immune responses, including those resulting from RNA viruses such as vesicular stomatitis, Sendai, West Nile, and dengue virus infection, repressing viral replication. Following viral infection, UBXN1 is induced, binds to MAVS, interferes with intracellular MAVS oligomerization, and disrupts the MAVS/TRAF3/TRAF6 signalosome. These findings underscore a critical role of UBXN1 in the modulation of a major antiviral signaling pathway.
Project description:Mitochondrial antiviral signaling protein (MAVS), an adaptor protein, is activated by RIG-I, which is critical for an effective innate immune response to infection by various RNA viruses. Viral infection causes the RIG-I-like receptor (RLR) to recognize pathogen-derived dsRNA and then becomes activated to promote prion-like aggregation and activation of MAVS. Subsequently, through the recruitment of TRAF proteins, MAVS activates two signaling pathways mediated by TBK1-IRF3 and IKK- NF-κb, respectively, and turns on type I interferon and proinflammatory cytokines. This study discovered that NEDD4 binding protein 3 (N4BP3) is a positive regulator of the RLR signaling pathway by targeting MAVS. Overexpression of N4BP3 promoted virus-induced activation of the interferon-β (IFN-β) promoter and interferon-stimulated response element (ISRE). Further experiments showed that knockdown or knockout N4BP3 impaired RIG-I-like receptor (RLR)-mediated innate immune response, induction of downstream antiviral genes, and cellular antiviral responses. We also detected that N4BP3 could accelerate the interaction between MAVS and TRAF2. Related experiments revealed that N4BP3 could facilitate the ubiquitination modification of MAVS. These findings suggest that N4BP3 is a critical component of the RIG-I-like receptor (RLR)-mediated innate immune response by targeting MAVS, which also provided insight into the mechanisms of innate antiviral responses.
Project description:RNA helicases play an important role in the response to microbial infection. Retinoic acid inducible gene-I (RIG-I) and members of the RIG-I-like receptor (RLR) family of helicases function as cytoplasmic pattern recognition receptors (PRRs) whose actions are essential for recognition of RNA viruses. RIG-I association with pathogen-associated molecular patterns (PAMPs) within viral RNA leads to its activation and signaling via the mitochondrial antiviral signaling (MAVS) adapter protein. This interaction mediates downstream signaling events that drive the innate immune response to virus infection. Here we identify the DEAH-box RNA helicase DHX15 as a RLR binding partner and signaling cofactor. In human cells, DHX15 is required for virus-induced RLR signaling of innate immune gene expression. Knockdown of DHX15 increased susceptibility to infection by RNA viruses of diverse genera, including Paramyxoviridae, Rhabdoviridae, and Picornaviridae. DHX15 associates with RIG-I caspase activation and recruitment domains (CARDs) through its amino terminus, in which the complex is recruited to MAVS on virus infection. Importantly, although DHX15 cannot substitute for RIG-I in innate immune signaling, DHX15 selectively binds PAMP RNA to promote RIG-I ATP hydrolysis and signaling activation in response to viral RNA. Our results define DHX15 as a coreceptor required for RLR innate immune responses to control RNA virus infection.
Project description:RNA virus invasion induces a cytosolic RIG-I-like receptor (RLR) signaling pathway by promoting assembly of the Mitochondrial antiviral-signaling protein (MAVS) signalosome and triggers the rapid production of type I interferons (IFNs) and proinflammatory cytokines. During this process, the pivotal kinase TANK binding kinase 1 (TBK1) is recruited to the MAVS signalosome to transduce a robust innate antiviral immune response by phosphorylating transcription factors interferon regulatory factor 3 (IRF3) and nuclear factor (NF)-?B and promoting their nuclear translocation. However, the molecular mechanisms underlying the negative regulation of TBK1 are largely unknown. In the present study, we found that THO complex subunit 7 homolog (THOC7) negatively regulated the cellular antiviral response by promoting the proteasomal degradation of TBK1. THOC7 overexpression potently inhibited Sendai virus- or polyI:C-induced IRF3 dimerization and phosphorylation and IFN-? production. In contrast, THOC7 knockdown had the opposite effects. Moreover, we simulated a node-activated pathway to show that THOC7 regulated the RIG-I-like receptors (RLR)-/MAVS-dependent signaling cascade at the TBK1 level. Furthermore, THOC7 was involved in the MAVS signalosome and promoted TBK1 degradation by increasing its K48 ubiquitin-associated polyubiquitination. Together, these findings suggest that THOC7 negatively regulates type I IFN production by promoting TBK1 proteasomal degradation, thus improving our understanding of innate antiviral immune responses.
Project description:The family Arenaviridae includes several important human pathogens that can cause severe hemorrhagic fever and greatly threaten public health. As a major component of the innate immune system, the RLR/MAVS signaling pathway is involved in recognizing viral components and initiating antiviral activity. It has been reported that arenavirus infection can suppress the innate immune response, and NP and Z proteins of pathogenic arenaviruses can disrupt RLR/MAVS signaling, thus inhibiting production of type I interferon (IFN-I). However, recent studies have shown elevated IFN-I levels in certain arenavirus-infected cells. The mechanism by which arenavirus infection induces IFN-I responses remains unclear. In this study, we determined that the L polymerase (Lp) of Mopeia virus (MOPV), an Old World (OW) arenavirus, can activate the RLR/MAVS pathway and thus induce the production of IFN-I. This activation is associated with the RNA-dependent RNA polymerase activity of Lp. This study provides a foundation for further studies of interactions between arenaviruses and the innate immune system and for the elucidation of arenavirus pathogenesis. IMPORTANCE:Distinct innate immune responses are observed when hosts are infected with different arenaviruses. It has been widely accepted that NP and certain Z proteins of arenaviruses inhibit the RLR/MAVS signaling pathway. The viral components responsible for the activation of the RLR/MAVS signaling pathway remain to be determined. In the current study, we demonstrate for the first time that the Lp of MOPV, an OW arenavirus, can activate the RLR/MAVS signaling pathway and thus induce the production of IFN-I. Based on our results, we proposed that dynamic interactions exist among Lp-produced RNA, NP, and the RLR/MAVS signaling pathway, and the outcome of these interactions may determine the final IFN-I response pattern: elevated or reduced. Our study provides a possible explanation for how IFN-I can become activated during arenavirus infection and may help us gain insights into the interactions that form between different arenavirus components and the innate immune system.
Project description:The unprecedented 2013-2016 outbreak of Ebola virus (EBOV) resulted in over 11,300 human deaths. Host resistance to RNA viruses requires RIG-I-like receptor (RLR) signaling through the adaptor protein, mitochondrial antiviral signaling protein (MAVS), but the role of RLR-MAVS in orchestrating anti-EBOV responses in vivo is not known. Here we apply a systems approach to MAVS-/- mice infected with either wild-type or mouse-adapted EBOV. MAVS controlled EBOV replication through the expression of IFN?, regulation of inflammatory responses in the spleen, and prevention of cell death in the liver, with macrophages implicated as a major cell type influencing host resistance. A dominant role for RLR signaling in macrophages was confirmed following conditional MAVS deletion in LysM+ myeloid cells. These findings reveal tissue-specific MAVS-dependent transcriptional pathways associated with resistance to EBOV, and they demonstrate that EBOV adaptation to cause disease in mice involves changes in two distinct events, RLR-MAVS antagonism and suppression of RLR-independent IFN-I responses.
Project description:Flaviviruses have evolved complex mechanisms to evade the mammalian host immune systems including the RIG-I (retinoic acid-inducible gene I) like receptor (RLR) signaling. Zika virus (ZIKV) is a re-emerging flavivirus that is associated with severe neonatal microcephaly and adult Guillain-Barre syndrome. However, the molecular mechanisms underlying ZIKV pathogenesis remain poorly defined. Here we report that ZIKV non-structural protein 4A (NS4A) impairs the RLR-mitochondrial antiviral-signaling protein (MAVS) interaction and subsequent induction of antiviral immune responses. In human trophoblasts, both RIG-I and melanoma differentiation-associated protein 5 (MDA5) contribute to type I interferon (IFN) induction and control ZIKV replication. Type I IFN induction by ZIKV is almost completely abolished in MAVS-/- cells. NS4A represses RLR-, but not Toll-like receptor-mediated immune responses. NS4A specifically binds the N-terminal caspase activation and recruitment domain (CARD) of MAVS and thus blocks its accessibility by RLRs. Our study provides in-depth understanding of the molecular mechanisms of immune evasion by ZIKV and its pathogenesis.
Project description:Strong innate and adaptive immune responses are paramount in combating viral infections. Dendritic cells (DCs) detect viral infections via cytosolic RIG-I like receptors (RLRs) RIG-I and MDA5 leading to MAVS-induced immunity. The DEAD-box RNA helicase DDX3 senses abortive human immunodeficiency virus 1 (HIV-1) transcripts and induces MAVS-dependent type I interferon (IFN) responses, suggesting that abortive HIV-1 RNA transcripts induce antiviral immunity. Little is known about the induction of antiviral immunity by DDX3-ligand abortive HIV-1 RNA. Here we synthesized a 58 nucleotide-long capped RNA (HIV-1 Cap-RNA58) that mimics abortive HIV-1 RNA transcripts. HIV-1 Cap-RNA58 induced potent type I IFN responses in monocyte-derived DCs, monocytes, macrophages and primary CD1c+ DCs. Compared with RLR agonist poly-I:C, HIV-1 Cap-RNA58 induced comparable levels of type I IFN responses, identifying HIV-1 Cap-RNA58 as a potent trigger of antiviral immunity. In monocyte-derived DCs, HIV-1 Cap-RNA58 activated the transcription factors IRF3 and NF-?B. Moreover, HIV-1 Cap-RNA58 induced DC maturation and the expression of pro-inflammatory cytokines. HIV-1 Cap-RNA58-stimulated DCs induced proliferation of CD4+ and CD8+ T cells and differentiated naïve T helper (TH) cells toward a TH2 phenotype. Importantly, treatment of DCs with HIV-1 Cap-RNA58 resulted in an efficient antiviral innate immune response that reduced ongoing HIV-1 replication in DCs. Our data strongly suggest that HIV-1 Cap-RNA58 induces potent innate and adaptive immune responses, making it an interesting addition in vaccine design strategies.
Project description:As the world faces the challenge of the COVID-19 pandemic, it has become an urgent need of the hour to understand how our immune system sense and respond to RNA viruses that are often life-threatening. While most vaccine strategies for these viruses are developed around a programmed antibody response, relatively less attention is paid to our innate immune defenses that can determine the outcome of a viral infection via the production of antiviral cytokines like Type I Interferons. However, it is becoming increasingly evident that the "cytokine storm" induced by aberrant activation of the innate immune response against a viral pathogen may sometimes offer replicative advantage to the virus thus promoting disease pathogenesis. Thus, it is important to fine tune the responses of the innate immune network that can be achieved via a deeper insight into the candidate molecules involved. Several pattern recognition receptors (PRRs) like the Toll like receptors (TLRs), NOD-like receptors (NLRs), and the retinoic acid inducible gene-I (RIG-I) like receptors (RLRs) recognize cytosolic RNA viruses and mount an antiviral immune response. RLRs recognize invasive viral RNA produced during infection and mediate the induction of Type I Interferons via the mitochondrial antiviral signaling (MAVS) molecule. It is an intriguing fact that the mitochondrion, one of the cell's most vital organelle, has evolved to be a central hub in this antiviral defense. However, cytokine responses and interferon signaling via MAVS signalosome at the mitochondria must be tightly regulated to prevent overactivation of the immune responses. This review focuses on our current understanding of the innate immune sensing of the host mitochondria by the RLR-MAVS signalosome and its specificity against some of the emerging/re-emerging RNA viruses like Ebola, Zika, Influenza A virus (IAV), and severe acute respiratory syndrome-coronavirus (SARS-CoV) that may expand our understanding for novel pharmaceutical development.
Project description:Cytosolic RNA sensing is a prerequisite for initiation of innate immune response against RNA viral pathogens. Signaling through RIG-I (retinoic acid-inducible gene I)-like receptors (RLRs) to TBK1 (Tank-binding kinase 1)/IKK? (I?B kinase ?) kinases is transduced by mitochondria-associated MAVS (mitochondrial antiviral signaling protein). However, the precise mechanism of how MAVS-mediated TBK1/IKK? activation is strictly controlled still remains obscure. We reported that protein phosphatase magnesium-dependent 1A (PPM1A; also known as PP2C?), depending on its catalytic ability, dampened the RLR-IRF3 (interferon regulatory factor 3) axis to silence cytosolic RNA sensing signaling. We demonstrated that PPM1A was an inherent partner of the TBK1/IKK? complex, targeted both MAVS and TBK1/IKK? for dephosphorylation, and thus disrupted MAVS-driven formation of signaling complex. Conversely, a high level of MAVS can dissociate the TBK1/PPM1A complex to override PPM1A-mediated inhibition. Loss of PPM1A through gene ablation in human embryonic kidney 293 cells and mouse primary macrophages enabled robustly enhanced antiviral responses. Consequently, Ppm1a(-/-) mice resisted to RNA virus attack, and transgenic zebrafish expressing PPM1A displayed profoundly increased RNA virus vulnerability. These findings identify PPM1A as the first known phosphatase of MAVS and elucidate the physiological function of PPM1A in antiviral immunity on whole animals.
Project description:Mitochondrial antiviral signaling protein (MAVS) is a critical innate immune signaling protein that directs the actions of the RIG-I-like receptor (RLR) signaling pathway of RNA virus recognition and initiation of anti-viral immunity against West Nile virus (WNV). In the absence of MAVS, mice die more rapidly after infection with the pathogenic WNV-Texas (TX) strain, but also produce elevated WNV-specific IgG concomitant with increased viral burden. Here we investigated whether there was a B cell intrinsic role for MAVS during the development of protective humoral immunity following WNV infection. MAVS-/- mice survived infection from the non-pathogenic WNV-Madagascar (MAD) strain, with limited signs of disease. Compared to wildtype (WT) controls, WNV-MAD-infected MAVS-/- mice had elevated serum neutralizing antibodies, splenic germinal center B cells, plasma cells and effector T cells. We found that when rechallenged with the normally lethal WNV-TX, MAVS-/- mice previously infected with WNV-MAD were protected from disease. Thus, protective humoral and cellular immune responses can be generated in absence of MAVS. Mice with a conditional deletion of MAVS only in CD11c+ dendritic cells phenocopied MAVS whole body knockout mice in their humoral responses to WNV-MAD, displaying elevated virus titers and neutralizing antibodies. Conversely, a B cell-specific deletion of MAVS had no effect on immune responses to WNV-MAD compared to WT controls. Thus, MAVS in dendritic cells is required to control WNV replication and thereby regulate downstream humoral immune responses.